Muzzle brakes have been used for many years to reduce recoil and improve the accuracy of firearms such as pistols, rifles, shotguns and artillery pieces. A muzzle brake is a portion of the gun barrel, or an extension of the barrel, which is provided with one or more (usually several) holes or vent apertures passing radially through the wall of the muzzle brake. If the muzzle brake is an integral part of the barrel, the apertures are typically located at or near the muzzle. If the brake is an attachment or extension of the barrel, usually a tubular body with a bore greater than the bore of the barrel, it is typically attached to the barrel at or near the muzzle. As used herein, the term "muzzle brake" shall generally refer to both integral and attached brakes. The term "muzzle brake" as used herein also includes devices such as "flash suppressors/hiders" and "compensators" to the extent they produce an elongated pattern of radially vented gas.
As a bullet or projectile travels down the firearm barrel after firing, the vent apertures allow the compressed air being pushed ahead of the bullet to escape from the muzzle brake in a lateral direction before the bullet reaches the apertures. Likewise, the vent apertures allow the high pressure combustion gas propelling the bullet to escape from the muzzle brake in a radial direction after the bullet has passed the vent apertures but before it exits the muzzle brake. By providing a decrease in the pressure of the gas both in front of and behind the projectile before it exits the muzzle brake, the recoil forces which accompany the firing of a gun are reduced. Muzzle brakes can also improve accuracy by decreasing the destabilizing effect which the high pressure gas has on the projectile immediately after it exits the muzzle.
A muzzle brake may be formed integrally with a gun barrel by drilling or otherwise forming vent apertures in the barrel itself. To achieve the greatest reduction and recoil, such brakes are most commonly formed at or near the muzzle of the gun barrel. However, brakes are sometimes formed at positions more rearwardly on the barrel. Alternatively, a muzzle brake may be fabricated as a unit separate from the gun barrel and attached thereto over the muzzle end to form an extension of the barrel. Muzzle brakes of this type are commonly attached to a gun barrel, for example, by cooperating threads formed on the inside of the muzzle brake and the outside of the barrel.
Most muzzle brakes employ an axial array of vent apertures, i.e., multiple axially spaced apertures or sets of apertures, or a single set of axially elongated apertures. This results in an elongated pattern of radially vented gas with different pressure characteristics from the rearward to the forward regions of the muzzle brake.
It has been found that a muzzle brake provides greater recoil reduction and accuracy improvement if the gas pressures in front of and behind the projectile are allowed to decrease uniformly over the length of the brake as the projectile approaches and passes therethrough. U.S. Pat. Nos. 4,930,396, issued Jun. 5, 1990 and 5,305,677, issued Apr. 26, 1994 both teach muzzle brakes which attempt to regulate the amount of pressure drop taking place along the length of the brake by varying the diameter of its internal bore. In the '396 patent the muzzle brake has an internal bore comprising several conical sections of varying size and configurations, while the brake of the '677 patent features several cylindrical bore sections which decrease in diameter toward the forward end of the brake.
Muzzle brakes are known to increase noise to the shooter, the result of the radial re-direction of gas upon firing. Some known muzzle brakes feature externally mounted blast deflectors which shield the shooter from some of this noise. In U.S. Pat. No. 5,063,827 issued Nov. 12, 1991 a blast deflector is fitted to the extreme rear end of a muzzle brake, where it attaches to the gun barrel. This blast deflector has an angled or concave surface facing the forward or muzzle end of the brake and is intended to deflect the combustion gases and sonic waves associated therewith forward away from the shooter. The deflector has no beneficial effect in terms of recoil reduction or improved accuracy, but rather is intended solely to decrease the annoying and possibly ear-damaging effects of the muzzle blast.
A muzzle brake disclosed in U.S. Pat. No. 4,869,151 attempts to reduce recoil as well as suppress noise. It features a plurality of apertures which angle forward as they pass from the interior bore to the surface of the muzzle brake. An annular rib is located immediately behind the vent apertures to partially shield the shooter from sound waves exiting therefrom.
U.S. Pat. No. 5,036,747 teaches a muzzle brake having forward slanting apertures which direct the gases escaping from the bore onto rearward sloping circumferential skirts. The impingement of gases on the skirts causes a forward thrust on the muzzle brake and hence the rifle barrel, the thrust tending to counteract recoil. The skirts also define plenum chambers which act to restrain the gases inside the muzzle brake for a pressure metering effect.
Muzzle brakes can also have an impact on gun accuracy by affecting barrel harmonics. The barrel of a firearm has a number of natural vibrational frequencies, or harmonics, one or more of which may be excited by firing of the weapon. Most gun barrels are stiff and highly damped, but harmonic vibrations cannot be completely eliminated and the muzzle of the barrel may still deflect enough upon firing to spoil the gun's accuracy.
The exact effect of barrel harmonic vibrations on projectile accuracy is difficult to predict, especially as it depends on the cartridge being fired, i.e., the weight of the projectile and the amount of propellant providing the thrust, as well as the weight and size of the barrel. This has led to the advent of muzzle brakes that are adjustable, allowing the shooter to close and open some of the vent apertures or to move the muzzle brake forward and rearward with respect to the barrel. This creates small changes in the barrel harmonics, and the shooter may use trial-and-error testing to find a muzzle brake setting that provides the best accuracy for a given rifle and cartridge combination. Examples of adjustable muzzle brakes are the BOSS System sold by Browning and the Adjustable Muzzle Brake sold by Que Industries.